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71.
G. Gaina V. Gaina A. Stoleriu C. Chiriac V. Cozan M. Sava 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1755-1768
Abstract New poly[N-(ester)-3-(ether)-4-(chloro)]maleimides were synthesized by the reaction of N-(4-chlorocarbonylphenyl)-3,4-dichloromaleimide (3) with various bisphenols such as hydroquinone (8a), 2,2-bis-(4-hydroxyphenyl)propane (8b), 4,4′ -(hexafluoroisopropylidene)diphenol (8c), and 2,5-bis(4-hydroxybenzylidene)cyclopentanone (8d). The structures of the resulted polymers were confirmed by IR and elemental analyses. A series of model compounds (4–7) was synthesized to facilitate confirmation of the structure of the polymers. The polymer containing hydroquinone units (9a) exhibited LC behavior in the melt, as observed by PLM measurements. 相似文献
72.
Yu. M. Chumakov Yu. A. Simonov S. G. Soboleva V. M. Sava S. A. Andronati M. Gdaniec 《Supramolecular chemistry》2013,25(2):225-227
Abstract X-ray crystallography, quantum-chemical calculations and conformational analysis have been employed to study chlorophenyl(piperazinylalkyl)phthalimides, potential ligands of 5-HT1A receptor. The molecular recognition of investigated compounds by 5-HT1Aserotonin receptor has been estimated according to their ability to inhibit the [3H8]-DPAT binding. The model for 5-HT1A pharmacophore has been proposed based on crystal structures of N-(aryl)piperazinyl — alkylphthalimides. 相似文献
73.
Ion Sava Ştefan Chişcă Maria Brumă Gabriela Lisa 《Journal of Thermal Analysis and Calorimetry》2011,104(3):1135-1143
The processing of polyimide films from polyamidic acid solutions involves the simultaeous loss of solvent and chemical conversion,
and may imply structural reorganization such as orientation or crystallization. The effect of thermal treatment on the thermal,
mechanical and dielectric properties of polymer films based on benzophenonetetracarboxylic dianhydride and 4,4’-diamino-3,3’-dimethyl
diphenylmethane have been investigated. The thermal treatment of polyamidic acid at different temperatures led to compounds
with different degree of imidization; it turned out that the imidization process took place with high speed until 240 °C and
then remained constant. The dynamic mechanical analysis (DMA), contact angles, and dielectric measurements revealed that the
storage modulus and contact angles increased with increasing of curing temperature while the dielectric constant decreased. 相似文献
74.
We consider a manufacturer who sells both the new and remanufactured versions of a product over its life cycle. The manufacturer’s profit depends crucially on her ability to synchronize product returns with the sales of the remanufactured product. This gives rise to a challenging dynamic optimization problem where the size of both the market and the user pool are dynamic and their current values depend on the entire history. We provide an analytical characterization of the manufacturer’s optimal pricing, production, and inventory policies which lead to a practical threshold policy with a small optimality gap. In addition, our analysis offers a number of interesting insights. First, the timing of remanufacturing activity and its co-occurrence with new product manufacturing critically depends on remanufacturing cost benefits, attractiveness of the remanufactured product and product return rate. Second, there is a small upward jump in the price of the new product when remanufacturing is introduced. Third, the manufacturer keeps the new product longer on the market as the cost of remanufacturing decreases. Fourth, partially satisfying demand for the remanufactured item is never optimal, i.e., it is satisfied either fully or not at all. Finally, user pool and inventory of returned products are substitutes in ensuring the supply for future remanufacturing. 相似文献
75.
Yi-Gui Wang Ericka C. Barnes Savaș Kaya Vinit Sharma 《Journal of computational chemistry》2019,40(31):2761-2777
The model reactions CH3X + (NH—CH=O)M ➔ CH3—NH—NH═O or NH═CH—O—CH3 + MX (M = none, Li, Na, K, Ag, Cu; X = F, Cl, Br) are investigated to demonstrate the feasibility of Marcus theory and the hard and soft acids and bases (HSAB) principle in predicting the reactivity of ambident nucleophiles. The delocalization indices (DI) are defined in the framework of the quantum theory of atoms in molecules (QT-AIM), and are used as the scale of softness in the HSAB principle. To react with the ambident nucleophile NH═CH—O−, the carbocation H3C+ from CH3X (F, Cl, Br) is actually a borderline acid according to the DI values of the forming C…N and C…O bonds in the transition states (between 0.25 and 0.49), while the counter ions are divided into three groups according to the DI values of weak interactions involving M (M…X, M…N, and M…O): group I (M = none, and Me4N) basically show zero DI values; group II species (M = Li, Na, and K) have noticeable DI values but the magnitudes are usually less than 0.15; and group III species (M = Ag and Cu(I)) have significant DI values (0.30–0.61). On a relative basis, H3C+ is a soft acid with respect to group I and group II counter ions, and a hard acid with respect to group III counter ions. Therefore, N-regioselectivity is found in the presence of group I and group II counter ions (M = Me4N, Li, Na, K), while O-regioselectivity is observed in the presence of the group III counter ions (M = Ag, and Cu(I)). The hardness of atoms, groups, and molecules is also calculated with new functions that depend on ionization potential (I) and electron affinity (A) and use the atomic charges obtained from localization indices (LI), so that the regioselectivity is explained by the atomic hardness of reactive nitrogen atoms in the transition states according to the maximum hardness principle (MHP). The exact Marcus equation is derived from the simple harmonic potential energy parabola, so that the concepts of activation free energy, intrinsic activation barrier, and reaction energy are completely connected. The required intrinsic activation barriers can be either estimated from ab initio calculations on reactant, transition state, and product of the model reactions, or calculated from identity reactions. The counter ions stabilize the reactant through bridging N- and O-site of reactant of identity reactions, so that the intrinsic barriers for the salts are higher than those for free ambident anions, which is explained by the increased reorganization parameter Δr. The proper application of Marcus theory should quantitatively consider all three terms of Marcus equation, and reliably represent the results with potential energy parabolas for reactants and all products. For the model reactions, both Marcus theory and HSAB principle/MHP principle predict the N-regioselectivity when M = none, Me4N, Li, Na, K, and the O-regioselectivity when M = Ag and Cu(I). © 2019 Wiley Periodicals, Inc. 相似文献
76.
Split-screen single-camera stereoscopic PIV application to a turbulent confined swirling layer with free surface 总被引:1,自引:1,他引:0
An annular liquid wall jet, or vortex tube, generated by helical injection inside a tube is studied experimentally as a possible
means of fusion reactor shielding. The hollow confined vortex/swirling layer exhibits simultaneously all the complexities
of swirling turbulence, free surface, droplet formation, bubble entrapment; all posing challenging diagnostic issues. The
construction of flow apparatus and the choice of working liquid and seeding particles facilitate unimpeded optical access
to the flow field. A split-screen, single-camera stereoscopic particle image velocimetry (SPIV) scheme is employed for flow
field characterization. Image calibration and free surface identification issues are discussed. The interference in measurements
of laser beam reflection at the interface are identified and discussed. Selected velocity measurements and turbulence statistics
are presented at
Re\uplambda=70 \hbox{Re}_{\uplambda}=70 (Re = 3500 based on mean layer thickness). 相似文献
77.
This paper presents the following definitions which is a natural combination of the definition for asymptotically equivalent,
statistically limit, lacunary sequences, and σ-convergence. Let ϑ be a lacunary sequence; Two nonnegative sequences [x] and [y] are S
σ,8-asymptotically equivalent of multiple L provided that for every ε > 0
uniformly in m = 1, 2, 3, ..., (denoted by x
y) simply S
σ,8-asymptotically equivalent, if L = 1. Using this definition we shall prove S
σ,8-asymptotically equivalent analogues of Fridy and Orhan’s theorems in [5] and analogues results of Das and Patel in [1] shall
also be presented. 相似文献
78.
We have investigated the effect of thermal annealing on the structure of single and stacked phase change memory films based on SnSe and GaSb. Samples were prepared by pulsed laser deposition and investigated by X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) methods. Electrical resistance versus temperature investigations showed crystallisation temperatures of 292°C and 198°C for SnSe and GaSb single films, respectively. Above the transition temperature, GaSb crystallises into a face-centered cubic structure, whereas SnSe has an orthorhombic arrangement. Annealing at three temperatures (160°C, 250°C and 350°C) of the SnSe\GaSb stacked films promotes bond breaking, atom diffusion between the two layers and formation of new phases. At 160°C, GaSb films crystallise partially and no effect is observed on the crystallinity of SnSe films. After 250°C, rhombohedral SnSb emerges in addition to GaSb complete crystallisation. A major, completely new, body-centered orthorhombic unindexed quaternary Ga-Sn-Sb-Se phase formation was observed in the samples annealed at 350°C. The GaSb crystallites are fully dissolved and we have observed the formation of a minor hexagonal SnSe2 phase. The analysis of EXAFS data, measured at Se and Ga K-edges, revealed changes in the local atomic environment as a function of the annealing temperature. A tetrahedral configuration is obtained for the Ga atoms in both as-deposited and annealed samples, whereas Se is mostly bivalent in the amorphous samples and has an octahedral arrangement in crystalline SnSe. Our results show that inter-layer diffusion should always be considered and evaluated when designing memory cells composed of stacked phase change chalcogenide films. 相似文献
79.
Savaş Kaya 《Molecular physics》2018,116(13):1677-1681
A new theoretical route employing the concept of chemical hardness has been developed to predict the surface tension γ and the changes of the standard enthalpies (CSEs) of sublimation ΔsH0 of alkali halides. The values of these quantities have been calculated by means of the ratios ηM/V1/3m where ηM and Vm are the molecular hardness and molecular volume, respectively. The obtained results have been compared with those of previous theoretical models as well as with experimental data. 相似文献
80.
We investigate spin conductance in zigzag graphene nanoribbons and propose a spin injection mechanism based only on graphitic nanostructures. We find that nanoribbons with atomically straight, symmetric edges show zero spin conductance but nonzero spin Hall conductance. Only nanoribbons with asymmetrically shaped edges give rise to a finite spin conductance and can be used for spin injection into graphene. Furthermore, nanoribbons with rough edges exhibit mesoscopic spin conductance fluctuations with a universal value of rmsG_{s} approximately 0.4e/4pi. 相似文献